The subject matter of this disclosure relates generally to photovoltaic (PV) power, and more particularly, to a system and method of filtering PV signals online to provide reactive power compensation by a PV inverter.
Reactive power compensation is a measure commonly employed for indirect voltage regulation. Modern PV inverters are required to have reactive power capabilities, and can therefore provide reactive power support. One method of reactive power compensation utilizes closed-loop voltage control by the PV inverters. The closed-loop controller automatically achieves and maintains the desired set point voltage at the point of interconnection (POI). It does this by comparing the actual voltage value measured at the POI with the voltage set point value, and adjusting the reactive power output of the PV inverter to minimize the error signal, which is the difference between the measured value and the reference value. In other words, a closed-loop controller is a fully automatic control system in which the reactive power compensation by the PV inverter is a function of the difference between the set point voltage and the measured voltage at the POI. A closed-loop voltage controller however may adversely interact with other PV inverter voltage controllers and capacitor back controls, as well as with On-Load Tap Changing (OLTC) transformers and voltage regulators.
An alternative method of reactive power compensation utilizes open-loop voltage control, where the reactive power compensation by the PV inverter is a function of its active power output. The PV inverter in this instance aims at compensating only the voltage variation caused by its own active power supply, without utilizing any closed-loop voltage control. A constant power factor reactive power compensation technique provides the simplest method of implementing open-loop compensation. More complex methods with higher compensation accuracy, such as variable power factor compensation, also exist. These reactive power compensation techniques, however, usually lead to a large amount of reactive power and therefore increased network losses.
Another measure for dealing with voltage variations in distribution networks utilizes OLTC transformers and voltage regulators. OLTCs enable a direct voltage regulation and therefore have the advantage of not injecting additional reactive power into the network, which would in most cases increase the system losses and reduce the transmission capacity of the network. Dealing with voltage variations caused by PV power generation is however a challenge, due to the slow reaction time associated with OLTC voltage compensation compared to the faster variation in PV power output due to cloud movement. A further challenge is associated with the extra wear and the lifetime reduction of the mechanical tap changers due to the high variability of PV power which could dramatically increase the number of tap changing actions.
In view of the foregoing, there is a need for a method of providing reactive power compensation in a network without incurring the life reduction generally associated with OLTC due to an increased number of tap changing actions caused by fast PV power variations. Further, the method of providing reactive power compensation in a network should not incur additional network losses caused by large amounts of reactive power in the network.